Correlation of hardness and yield strength of titanium

Correlation of hardness and yield strength of titanium grade 2 Konrad Eiler 25/04/2016

Scope § Problem: Residual stress measurements on the He tank only valid up to 80% of the yield strength § 1 st step: Correlation of Vickers hardness and hardness of portable indenter (HLD) with yield stress of the base material with different initial thickness § 2 nd step: Translation of HLD values measured on the He tank into Vickers hardness and yield stress Konrad Eiler 2

Hardness and yield stress of base material Yield stress correlated with portable durometer hardness 370 360 350 Rp 0. 2 [MPa] Yield stress taken from tensile tests [1] correlated with HV 20 340 330 320 310 300 158 160 162 164 HV 20 166 168 170 450 460 470 480 490 500 510 520 HLD Konrad Eiler 3

Estimation of yield stress on the helium tank 370 360 Rp 0. 2 [MPa] 350 340 330 320 310 300 450 460 470 480 490 500 510 520 HLD Konrad Eiler 4

Estimated yield stress in distance from the weld 365 360 Rp 0. 2 [MPa] 355 350 345 340 335 330 325 0 2 4 6 8 10 12 14 16 18 20 X [mm] Konrad Eiler 5

Comments (1) § Measurements closer than 2. 5 mm from the weld extremity not possible § Problem: Measurement of portable hardness influenced by many factors, i. e. surface state, support, material thickness § Values have high deviation high uncertainty Konrad Eiler 6

Comments (2) § Linear correlation of yield and hardness is a fair assumption for estimation of the yield stress in the range of the reference values § Therefore, given yield stresses are only estimations and can give an orientation value § Base material was annealed local yield stress lower than 300 MPa not expected § If more accurate analysis is required (or closer to the weld), it should be done on cut pieces using the standardised Vickers hardness Konrad Eiler 7

References § [1] K. Eiler: Materials analysis Titanium Grade 2 for CRAB Cavity Helium Tank Prototype. EDMS 1538192, 2016. Konrad Eiler 8

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